Catalytic with hydrogen, 304 Biphasic reactions

More recently. Baker, Tumas, and co-workers published catalytic hydrogenation reactions in a biphasic reaction mixture consisting of the ionic liquid [BMIM][PFg] and SCCO2 [10]. In the hydrogenation of 1-decene with Wilkinson s catalyst [RhCl(PPh3)3] at 50 °C and 48 bar H2 (total pressure 207 bar), conversion of 98 %... 

A biphasic system consisting of the ionic liquid [BMIM]PF6 and water was used for the epoxidation reactions of a, 3-unsaturated carbonyl compounds with hydrogen peroxide as an oxidant at room temperature 202). This biphasic catalytic system compared favorably with the traditional phase transfer catalysts. For example, under similar conditions (15°C and a substrate/NaOH ratio of five), the [BMIM]PF6/H20 biphasic system showed a mesityl oxide conversion of 100% with 98% selectivity to oc, 3-epoxyketone, whereas the phase-transfer catalyst with tet-rabutylammonium bromide in a CH2CI2/H2O biphasic system gave a conversion of only 5% with 85% selectivity. 

NADP+ in a reaction with 2-propanol accompanied by formation of acetone as coproduct. Both ketone/alcohol reactions are equilibrium processes and therefore high 3delds of (f )-2-octanol are not available in a monophasic aqueous system, or in an organic-aqueous biphasic system where the partition coefficients of 2-propanol and acetone are approximately the same. It was found, however, that in a biphasic water/[bmim][(CF3S02)2N] system acetone was preferentially dissolved by the IL phase and this pulled the catalytic transfer hydrogenation of NADP+ by 2-propanol in the aqueous phase to near completion. Consequently, almost quantitative yields of (i )-2-octanol were obtained (275). 

The treatment of an orange solution of [IrCl(cod)]2 (cod=l,5-cydooctadiene) in l-butyl-3-methylimidazolium hexafluorophosphate with hydrogen at 75 °C for 10 min affords a black solution. This ionic solution promotes the biphasic hydrogenation of various olefins under mild reaction conditions, and the products were isolated almost quantitatively by simple decantation. The catalytic activity of this system is significantly superior to those obtained in biphasic conditions by classical transition-metal catalyst precursors in ionic liquids under similar reaction conditions. A mercury test clearly indicated the presence of lr(0) particles in the system formed by the reduction of the Ir(I) precursor in l-butyl-3-methylimidazolium hexafluorophosphate. These nanoparticles could be isolated by centrifugation from the catalytic mixture (Dupont et al., 2002). 

The first application involving a catalytic reaction in an ionic liquid and a subsequent extraction step with SCCO2 was reported by Jessop et al. in 2001 [9]. These authors described two different asymmetric hydrogenation reactions using [Ru(OAc)2(tolBINAP)] as catalyst dissolved in the ionic liquid [BMIM][PFg]. In the asymmetric hydrogenation of tiglic acid (Scheme 5.4-1), the reaction was carried out in a [BMIM][PF6]/water biphasic mixture with excellent yield and selectivity. When the reaction was complete, the product was isolated by SCCO2 extraction without contamination either by catalyst or by ionic liquid. 

The solid is used as a heterogeneous catalyst or as a water-soluble system in biphasic conditions in the hydrogenation of benzene and pheny-lacetylene [65]. The heterogeneous system Rh-PVP is investigated in the solid/liquid catalytic hydrogenation of benzene with a ratio of 1/34000 at 80 °C and 20 bar H2. The conversion into cyclohexane is about 60% after 200 h of reaction time. In a water/benzene biphasic condition at 30 °C and under 7 bar H2, complete hydrogenation (Scheme 2) for a molar ratio of 2000 is observed after 8 h giving a TOF = 675 h (related to H2 consumed), never-... 

Ru3(CO)12(117)3] and [H4Ru4(CO)11(117)] as catalyst precursors in the hydrogenation of non-activated alkenes under biphasic conditions. Each cluster displays activity under moderate conditions, ca. 60 atm. H2 at 60 °C with catalytic turnovers up to ca. 500. The trinuclear clusters undergo transformations during reaction but can be used repeatedly without loss of activity.325... 

Various other biphasic solutions to the separation problem are considered in other chapters of this book, but an especially attractive alternative was introduced by Horvath and co-workers in 1994.[1] He coined the term catalysis in the fluorous biphase and the process uses the temperature dependent miscibility of fluorinated solvents (organic solvents in which most or all of the hydrogen atoms have been replaced by fluorine atoms) with normal organic solvents, to provide a possible answer to the biphasic hydroformylation of long-chain alkenes. At temperatures close to the operating temperature of many catalytic reactions (60-120°C), the fluorous and organic solvents mix, but at temperatures near ambient they phase separate cleanly. Since that time, many other reactions have been demonstrated under fluorous biphasic conditions and these form the basis of this chapter. The subject has been comprehensively reviewed, [2-6] so this chapter gives an overview and finishes with some process considerations. 

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